Telephone diaphragm



MziySTIQZS. 1,536,486

H. FISCHER TELEPHONE DIAPHRAGM Filed 00%.. 24, 1922 w 2 Sheets-Sheet 1 IN VENTOR A TTORNEY5 H. FISCHER TELEFHONEDIAPHRKGM I Filed Oct. 24, 1922 2 Sheets-Sheet 2 INVENTOR IQ I u A TTOR NE Y5 Patented May 5, 1925.

UNITED STATES 1,536,486 PATENT OFFICEJQ HERMANN 215cm; on NEW YORK, N. Y., assronoa ro c. BBANDES, mc.,-a con;-

' roaarrou or NEW-YORK.

'mrasrnomz DIAPHRAGM.

Application and October 24, 1922. Serial No. 596,629.

To all whom it may concern: 'Be it knownthat'I, Hnm'raxx Fiscm-zn, a citizen of Ru$ia, residing at New York, in the county. of New York, State of New 5 York, have invented certain new and useful Im rovements in Telephone Diaphragms; an I do hereby dmlare-the following to be vention, such aswill enable others skilled in use the same. This invention relates to telephone receiver diaphragms for usein" double pole telephone receivers.

In telephonereceivers of the type referred to wherein two'poles of an elcctromagnet are disposed close relation to a sound producing magnetic diaphragm, it has been lo the art to which it appertains to malte and.

found that acertain amount of tone distor-' tion occurs, the extent of which is largely dependent upon the accuracy with which the instrument is constructed.

It has been found, that the distortion referred to is due, in part at least, to un-' 25' balanced synchronous action or unequal electromagnetic flux fields of the two electromagnet poles.- Ina double pole telephone receiver diaphragm-two quite distinct vibratory areas m created, .'ach resulting from v :m the clectromagn'eticaction of one of the poles. These two vibratory areas, in-so far as it has been possible to ascertain, inter fei'e at some point on the diaphragm, usually at the center portion, with the result that distortional vibrations are set, up. Those distortional vibrations, it will be understood, are due to the conjoint non-synchronous or unbalanced action of the two major vibratory areas.

One of the objects of this invention is to eliminate these distortional vibrations and thereby provide a telephone. rc'ecivcr having improved tonal qualities.

Experiments have. shown that a narrow aperture of suitable length in the center porti n of a diaphragm, so disposed as to etl'ert sub tantially a physical separation of the two vibratory areas, results in a material redu tion of distortion. The aperture in the diaphragm may be. strainor urrilin ar. or it may have. any ne. of sev ral suita le forms. It -is,"ho\\'e\'cr, preferable. that the aperture. he as narrow as practical considerations will permit, first because of the fact that it forms a break in the magnetic path of the receiver, and second because of the possibility of an excessive amount "of foreign matter entering the receiver-through the aperture if it; be of substantial width. Diaphragms in accordance w th this invcn-' -tion have been made with apertures of the a full, clear, and exact description of the in-- inercially practicable to provide there 'is'no appreciable increase in the reluctanceof the magnetic circuit.

. Apcrtures approximately corresponding in t'orm'tri the so-callcd f-holes which aieprovided in violins and some other musical iristrum-ants have been found particularly ad \antageous in connection with the present invention. A diaphragm having two such f-holes and intended for use. more particularly in a single pole telephone receiver is disclosed in my Patent 1,486,081, dated March 4, 1924. As explained in the aforementioned patent, 'a diaphragm provided with one. or more of the so-callcd f-holcs is rendered capable of more accurately reproducing both the upper and lower notes'of the. musical scale. The ordinar telephone. diaphragmas usually designed is more. capable of accurately reproducing the. higher n tes of the scale by reason of the. fact that the higher notes more clearly approach the natural period .of tiic diaphragm,- which is usually of the order of 800 or 900 cycles per second.

period otsurh diaphrag'ms, the lower notes are substantially attenuated, and accordingly the proportionate volume of all the original tones is not accurately maintained in reproduction.

A plain te.lephone. diaphragm of the ordinary typ'when modified in a cordance with the invention of my afor mcntionml copendiug application is capable. of reproducing tbc lowrr notes of the musical scale in materially greater proportionate volume without the.- reproduction of the higher notes being in any way ati'erted.

it has likewise been found that the. best results are obtained with the present inventioui as in that of my aforementioned eopending application, when the aperture is in the form o'f an f-hole similar to that of a violin, but preferably modified so that its width is as small as practical considerations d will permit.

Other forms of aperture, some of which are illustrated in the accompanying drawing, give very satisfactory 'results with a double pole receiver, but it'has been quite convincingly determined that the f-hole causes either in the transmitting or receiving form is superior to any other.

.Not all telephone distortion is due to inherent defects in receiver diaphragms; it may arise from any one or more of several station, and inthe case of wire telephony it may be caused by the transmission line. It

should not be presumed that a diaphragm C in accordance with the present invention traneous sources.

will correct distortion arising from such ex- Furtnermcre in the design of the-receiving instrument'itself there are. several important factors contributing to proper reproduction, which are quite d1stinct from what has already been pointed.

out. If the receiver is poorly designed, it cannot be expected that its defects will be cured by the use of a diaphragm in accordance with the present invention, although a material improvement may be realized in many instances in spite of weak design.

In the accompanying drawings, Fig. 1

illustrates a telephone diaphragm in accord.-

, ance with the preferred form of the invention; 1

Fig. 2 is a cross sectional yiew of=a double pole telephone receiver in which is incorp orated a diaphragm of the type shown in Fig. 3, illustrates a diaphragm constitutin a modified form of the invention;

ig. 4-illustrates another diaphragm constituting a modified form of the invention;

and. 5 illustrates still another modified form. I

The telephone receiver shown in cross section in Fig. 2 comprises a casing 1 in which is mounted a permanent magnet 2, having two polepieces '3 and 4, respectively, forming cores for the elcctromagnet windings 5 and 6. The diaphragm 7, which is preferably like that shown in Fig.1, is mounted in close juxtaposition to the ends of polepicccs 3 and 4, and cap 8 is provided '7, 8*, 9 and 10 are interposed in the ture 0 of wave form, and in Fig. 5 the dia phragni 10'is provided with a straight aperture 10.

. On account of the 'fact thatthe apertures ma netic path of the receiver, as will be readiIy reco nized, each of these apertures is pref-' erabIy" made as narrow as practical considerations will permit. B practical considerations is meant the piysical limitations imposed by reason of'the difliculty of producing extremely, narrow apertures commercially. In Fig. 5 the dotted lines represent approximately the two vibratory areas of the diaphragm which are individual to the polepieces 3 and t. Since one of the objects of this invention is to substantially prevent in torference between the two vibratory areas, it will be evident that the lengthwise dimension of the aperture should be snllicient to so function. It is, however, preferable that this dimension should not be greatly in-excessof this requirement, because the reluctance of the magnetic path of the receiver increases with any increase in the length 'of the aperture, due to the factthat part of the flux finds a path through the diaphragm beyond the extremities of the aperture, and any increase in the length of the aperture decreases this path.

()f the four forms of apertures shown,

Figs. 1, 3, 4 and 5, that of Fig. 5 is the least satisfactory. The apertures of Figs. 3 and 4 are about equal in effectiveness and are considerably better than that of F ig. 5,.

whileuthe f-hole of'Fig. 1 is substantially better than any of the other apertures, No exact dimensions of apertures appear to he essential to the successful operation of the invention, but it may be stated thatin experiments which have been conducted good results have been obtained with a diaphragm 2 1/8 in diameter and .006- thick in which the overall lengthwise dimension A of the f-hole (see Fig. 1) was approxi- 4 mately 11/32; the overall width B was approximately 3/32"; the width of the aperture was approximately 10/1000"; and

the diameter of the end openings approximately 3/64.. The. overall lengths of theaperturcs of Figs. 3, 4 and 5 may be ap proximately the same as that given for the overall length of the f-hole of Fig. 1. The

overall \\'idth\\-"ise dimensions may be proportionately as shown. It wil be understood that the dimensions suitable'in any particular case are dependent largely-upon the size of the magnet cores 3 and and the separation lhcrche'tween. In tlie' 'experimcnts referred to the lengthwise dimen-- sion G of each of the magnet cores was .565", the width D was .050", and the centcr-to-center dimension E was .375"-. At the present time the dimensions for each particular ease ean, be bestestablished by experiment, no empirieal rule having as yet been formulated. V P I According to the theory of the action-of the diaphragr ns 7', 8and 9 of Figs.- 1, 3 and -4 respectively, the'reason; for the lower :notespf the musical scale being accentuated is thatth integral projecting portions '--7'., 7, 8*, 8 and 9" have lower naturalperiods than the remaining portions of the .res I tive diaphragms. This theory seems to uive beenwvell established by the experiments which have been conducted, but its accuracy is not at all essential. to the complete disclosure of the invention, and it is not desired that this theory be construed as imposing any lirnitation upon the'seope of the invention. V The reason for the better-results b-- r 20 tained with the f-hole'o f' Fig than with t finperturcsof Figs. 3 and 4.is not well established but i't -is conjectured that. fur- :ther. experiments will 'show that a diamade which will give equaNy as good rephrafgm in accordance with Fig. 4 can lie sults as that of Fig. 1'.

d i r 1. In a telephone receiver. a diaphragm, a pair of elect-romagnet polcs'd-is ji-;se(l in operative relation toesaid diaphrainn, said dlaphragn'i being provided with.an Llnll:

- gated f-shaped aperture at its renter por- (ion dividing said diaphragm into two portions joined'on opposite ends of said elongated F shaped aperture forming L \\'u adjacentareas arrangedto be set into vibrati n by the actuation of said poles, said elon- 'gatedF shaped aperture operating to sub-- stantially prevent interference between the vibrations'set up in 'said amas'when said areas vibrate non-synehronously.' v 2. Iu a telephone receiver. a diaphragm" a,p'air of elei-timnagiiet poles disposed in operative ielation to said diaphrag lng saiddlaphragi'n being-provided with an elon-' gated aperture at its center portion consisting; of a narrow slot integral with said dia-' phragmand constantly varying diree' tmn, said slotthvnlnxgnud dlapliragntnito tuo portions joined on 'oppositeen rsof saidi elongated aprtum forming tu o'aidia- -c'nt art-as a rranged to hr: set into vibratioil by the aetuationfof saitLpoles, saidnarrow slotoperating to substantially prevent interft -renw hetween'the vibrations set lip in the respertiveareas. I

2 A telephone receiver. diaphragm harin}; an elongated aperture at its center por-.

tion eonsisting' of a single slot of varying direction llll(.;| :l l wlthsaid diaphragm.

ing an elongate'l apertnre-at its eenterportiouconsisting ofa slngzle slot having a constaut \v'ulth intermmhate the ends of, said slut and a substantially increased width at 1ucuimNN ISCHER.

. 6O 4. A telephone receiver diaphragnrhav-i gral and co-planar I 

